The present invention relates to lasers and in particular to a mode-locked laser providing multiple coincident beams of discrete different frequencies.
Many important applications for lasers require multiple laser beams having specific wavelengths. For example, U.S. Pat. No. 5,912,178 entitled: “Passive Measurement of Isotopes to Monitor Health”, assigned to the assignee of the present invention and hereby incorporated by reference, describes a system for monitoring the ratio of C12 to C13 in a patient's breath to establish the health of the patient. In this application, a first laser may provide a beam having a wavelength aligned with the C12 feature and a second laser may provide a beam having a wavelength aligned with the C13 feature. In addition, a third laser may provide a beam having an intermediate wavelength with negligible absorption by CO2 as a baseline reference.
In order to detect absorption of the laser light separately for each of these features, multiple optical paths and detectors may be used, or the laser is separated optically using filters or the like. The need for multiple lasers and associated optical components increases the cost and size of such systems.